This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for DIRECTLY HEATING ROLLER FOR FIXING A TONER IMAGE AND MANUFACTURING METHOD THEREOF earlier filed in the Korean Industrial Property Office on the Feb. 24, 2000 and on the Sep 2, 2000, and there duly assigned Ser. No. 9177/2000 and No. 51885/2000 respectively.
1. Field of the Invention
The present invention relates to a directly heating roller for fixing a toner image and manufacturing method thereof.
2. Description of the Related Art
In conventional electrophotographic copying machines, facsimiles, printers and related machines using an electrophotographic process, a charging roller uniformly charges a photoreceptor on an outer circumference of a photoreceptor drum by applying a high voltage when the charging roller is rotated. An electrostatic latent image is formed on the drum by scanning the surface of the photoreceptor through a laser scanning unit (LSU). Then, a visual image is developed through a developer by supplying a toner to the electrostatic latent image formed on the photoreceptor. Thereafter, an image formed by the toner is copied on a paper that passes between a copying roller and the photoreceptor drum by applying a copying voltage and by rotating them.
In order to fix the toner image, a conventional electrophotographic image forming apparatus uses a method of temporarily melting accumulated toner using a heating roller in a fixing portion of the image forming apparatus to apply heat to the paper. Generally, as a heat source of heating the heating roller at a predetermined temperature, a halogen lamp is installed in the heating roller.
A conventional electrophotographic image forming apparatus includes a paper outlet, a control panel, a control board cover, an upper cover opening button, a paper displaying window, a multipurpose paper feeding window, an auxiliary cassette, a paper cassette and a subsidiary support.
In operation of the apparatus, a toner is stirred by a stirrer in a toner cartridge. A toner-regulating blade regulates the amount of toner supplied and thus the toner is supplied through a supply roller. A charging roller uniformly charges a charge layer on the surface of a photoreceptor drum. A laser scanning unit forms a electrostatic latent image on the surface of the photoreceptor drum. A developing roller develops the toner on the electrostatic latent image formed on the surface of the photoreceptor drum. A copying roller copies a toner image formed on the surface of the photoreceptor drum onto a paper.
Thereafter, the paper on which the toner is attached is sent to a fixing portion, and when the paper passes between a heating roller and a pressure roller, the toner image in the form of a powder is melted and is fixed on the paper. In other words, the heating roller generates a heat when a voltage is applied to the halogen lamp. The toner is melted due to a fixing heat of the fixing roller and is fixed on the paper a pressure of the pressure roller. A thermistor located on the heating roller serves to maintain a constant temperature by sensing the temperature of the fixing roller.
The technology using a halogen lamp has a disadvantage that power consumption is high. One reason for the high power consumption is that this device requires a predetermined warming-up time when electrical power is supplied to form an image at a time after the electrophotographic image forming apparatus has been turned off. The predetermined time, which may range from tens of seconds to tens of minutes, must elapse after the start of supplying electrical power before the heating roller reaches a desired target fixing temperature. The conventional technology described above also requires that electrical power be applied even in a standby mode in order to maintain a constant roller temperature, which further increases the power consumption.
Another disadvantage is that it is very difficult to compensate for the decrease of the roller temperature due to heat loss to the paper which occurs when the heating roller contacts the paper. Furthermore, in order to print the next image, a predetermined standby time should be passed and, therefore an image can not be rapidly printed.
A different kind of heating roller of the conventional art, a directly-heating roller for fixing a toner image, is described in U.S. Pat. No. 4,776,070. This directly heating roller has a bonding layer deposited on a roller body, and a lower insulating layer deposited on the bonding layer. The lower insulating layer provides electrical insulation between the roller body and the layers above. A heat generating resistance layer is arranged on the lower insulating layer, and an upper insulating layer is arranged on the heat generating resistance layer. A protective layer is arranged on the upper insulating layer and serves to prevent an offset of the toner image from occurring. Electrode layers are arranged on axial end portions of the heat generating resistance layer and serve to provide electrical power to the heat generating resistance layer.
The heat generating resistance layer is described as made of a Nixe2x80x94Cr compound and a ceramic matrix formed from an alumina ceramic, and an arc-plasma spraying method is used to construct the heat generating layer. The bonding layer is described as a Nixe2x80x94Crxe2x80x94Mo, Nixe2x80x94Al or Nixe2x80x94Cr alloy which is plasma-sprayed so as to partially form an oxide.
This bonding layer is apparently required in order to bond the roller body to ceramic used in the lower insulating layer. However, even with the bonding layer, a separation between the layers may occur due to temperature characteristics between the two layers, or from applied pressure.
Based on my reading of the art, then, I have decided that what is needed is a better directly heating roller for use in electrophotographic devices.
It is therefore an object of the present invention to provide a directly heating roller for fixing a toner image and a method of manufacturing the same.
It is also an object of the invention to provide a directly heating roller have a short warming-up time, a low power consumption and a simple structure.
It is a further object to provide a directly heating roller which has excellent heat resistance and durability.
A yet further object of the invention is to provide a directly heating roller which does not suffer from separation between the roller body and an insulation layer on the roller.
A still further object of the invention is to provide a directly heating roller which is less expensive to manufacture.
In order to achieve the above objects, the present invention provides a directly heating roller for fixing a toner image, including a conductive roller body having a cylindrical cross section; an insulating layer formed by a heat-treatment at a first temperature less than an elastic is critical temperature of the roller body; a heat generating layer formed on the insulating layer by a heat-treatment at a second temperature less than the first temperature; a protection layer formed on the heat generating layer; and electrodes formed on both end portions of the heat generating layer.
The present invention further provides a method of manufacturing a directly heating roller for fixing a toner image including preparing a conductive roller body having a cylindrical cross section; depositing an insulating layer paste on an outer surface of the roller body in a predetermined thickness; forming an insulating layer by heating the insulating layer paste at a first temperature of less than an elastic limit temperature of the conductive cylindrical roller; depositing a heat generating layer paste on the surface of the insulating; forming a heat generating layer by heating the heat generating layer paste at a second temperature of less than the first temperature; forming a protection layer on the heat generating layer; and forming electrodes on both sides of the heat generating layer.
The present invention further provides a directly heating roller for fixing a toner image, including: an insulating roller body having a cylindrical cross section; a heat generating layer formed by depositing the heat generating layer paste on the roller body in the form of a paste and by heating the deposited heat generating layer paste at a temperature of less than the elastic critical temperature of the roller body; a protection layer formed on the heat generating layer; and electrodes electrically contacting to both end portions of the heat generating layer.
The present invention provides a method of manufacturing a directly heating roller for fixing a toner image, including: preparing an insulating roller body having a cylindrical cross section; depositing a heat generating layer paste on the surface of the roller body in a uniform thickness; forming a heat generating layer by heat-treating the heat generating layer paste at a predetermined temperature; forming a protection layer on the heat generating layer; and forming electrodes on both ends of the heat generating layer.
As described herein before, according to the embodiments of the present invention, it is possible to form a ruthenium-based heat generating layer on the surface of the roller and to make it to instantaneously reach a fixing temperature. As compared with the Nixe2x80x94Cr based resistive heat generating material according to the conventional art, it is possible to generate a target fixing temperature as soon as possible using a lower electrical power. Also, in forming a ruthenium-based electric resistance heat generating layer, since a process can be carried out at a temperature below 700xc2x0 C., below 600xc2x0 C., or even below 550xc2x0 C., and thus a wide range of materials may be selected for the roller body and the insulating layer. Accordingly, the manufacturing yields can be improved and cost can be reduced. Further, it is possible to manufacture a heat generating resistor layer having a uniform thickness. Furthermore, since it is possible to maintain the fixing temperature characteristics uniformly as a whole, and thus the toner fixing characteristics can be improved.